Conventionally, a resin circuit board is used as a circuit board on which a semiconductor element such as an IC (Integrated Circuit) and an LSI (Large Scale Integration) is mounted.
The circuit board includes a through hole that penetrates in a vertical direction, a cylindrical through-hole conductor that is formed along an inner wall surface of the through hole, and a column-shaped insulator with which a region surrounded by the through-hole conductor is filled.
As illustrated in FIG. 10, the through hole can be made by drilling an insulating layer constituting the circuit board, and a through-hole conductor 11X can be plated on an inner wall surface of a through hole SX. A region surrounded by the through-hole conductor 11X is filled with a thermosetting resin, and the thermosetting resin is thermally cured to form an insulator 14X (see Japanese Unexamined Patent Publication No. 10-215042).
However, in the circuit board described in Japanese Unexamined Patent Publication No. 10-215042, the through-hole conductor is formed into a cylindrical shape, and the insulating layer constituting the circuit board differs from the through-hole conductor in a thermal expansion coefficient. Therefore, when heat is applied to the circuit board from the outside, occasionally the through-hole conductor is peeled off from the inner wall surface of the through hole.